1. Field of the Invention
The present invention relates to a gas turbine, and more particularly, to a gas turbine that cools a turbine rotor blade.
2. Description of the Related Art
Conventionally, a gas turbine is an apparatus that extracts energy from combustion gas generated by combusting air and fuel therein. A gas turbine rotates a turbine by using energy of combustion gas generated by combusting fuel and compressed air, and outputs rotation energy from the rotor. The combustion gas is, however, supplied to the turbine while the combustion gas is hot. Therefore, the rotor blade of the turbine is also exposed to hot atmosphere. To address the issue, for example in Japanese Patent Application Laid-open No. S61-226502, a gas turbine is disclosed in which, air is supplied from a compressor, which is a supply source of cooling air, to a rotor blade, which is a supply destination of cooling air, through a central hole or a hole provided along a central axis of a rotor thus the rotor blade is cooled.
In the technology described in Japanese Patent Application Laid-open No. S61-226502, air compressed by the compressor via the central hole of the rotor flows from the compressor to the turbine via an internal passage, and is thus supplied to the rotor blade as cooling air. In Japanese Patent Application Laid-open No. 61-226502, some of air is extracted from a disk or a rotating member of the compressor to a cavity located in the compressor, and is supplied to the rotor blade passage via the internal passage. Therefore, it is difficult to adjust amount of the extracted air while the gas turbine is in operation. Thus, during the maximum load operation, cooling air more than flow rate required for cooling the rotor blade may be extracted from the compressor. As a result, a thermal efficiency of the gas turbine may be reduced.
In the technology described in Japanese Patent Application Laid-open No. S59-41001, similar to the technology described in Japanese Patent Application Laid-open No. S61-226502, air is supplied from a compressor to a rotor blade through an internal passage. Thus, the technology described in Japanese Patent Application Laid-open No. S59-41001 also has the same problem. In the technology described in Japanese Patent Application Laid-open No. H11-117702, coolant is supplied from a turbine rotor shaft end. The technology is meant for recovery of coolant. Therefore an object thereof is not the same as that of the present application.
In general, amount of cooling air necessary for cooling the rotor blade differs in accordance with load of a gas turbine. More specifically, during high load operation, cooling capacity of a gas turbine needs to be increased by supplying high pressure air to a rotor blade and thus securing necessary amount of air. During low load operation, amount of cooling air needs to be reduced. Therefore, deterioration of thermal efficiency of the gas turbine needs to be prevented by supplying comparatively low pressure air thereto and thus preventing consuming unnecessary air. In Japanese Patent Application Laid-open No. H11-117702, any means is not disclosed for adjusting amount of air in a gas turbine in which load thereof fluctuates.